Whitehurst would downplay his injury afterward, but there was enough concern that the Chargers began making calls around the league, sending feelers to potential replacements, sources said.

Billy Volek naturally jumps out as possible candidate. He spent the past five years as a San Diego backup and remains a free agent after his March release.

Earlier this week, a league source said that Volek, 36, plans to continue his career and is on eight to nine teams' emergency list.

Jarrett Lee, an undrafted rookie from LSU, is the third quarterback in camp.

Whitehurst was able to walk off the practice field on his own power.

“I'll be all right,” he said in the locker room. “It's not bad.

Before being carted off, Gaither leaned forward as an athletic trainer pressed ice against his lower back. The 6-foot-9 lineman, who signed a four-year, $24.5 million contract in March, had what one teammate called a “full body cramp."

Depth, depth, depth.

It's been the chorus to an offseason that's seen the Chargers sign 20 veterans with at least four years of NFL experience. It's what they hope will be the difference in their campaign to end a two-year playoff drought.

They'd just rather not depend on it this soon.

With Gaither out, reserve Mario Henderson saw first-team reps at left tackle the rest of practice. It was a good test for the 335-pounder.

"That's what I'm trying to make the team to do," Henderson said. "To be a swing (tackle) or backup. So on the first day, let's show them. Show them right now. That's what I want to be. That's what they brought me in for. I can do it, left side or right side."

Injuries have reared their head around the Chargers in recent years. It's just one of those things.